Phase rotation detector and frequency regulator



Oct. 29, 1935. L. USSELMAN PHASE ROTATION DETECTOR AND FREQUENCYREGULATOR Filed Dec. 10, 1932 6 Sheets-Sheet 1 533$ K QQ INVENTOR GEORGEL. USSELMAN BY I ATTORNEY G. L. USSELMAN Oct. 29, 1935.

PHASE ROTATION DETECTOR AND FREQUENCY REGULATOR FiledDec. 10, 1932 v 6Sheets-Shet PHASE 190714770 05756701? (mm/r miaumci JOURCE INVENTORLGEORGE LUSSELMAN BY 4 q wvM/ ATTORNEY- Oct. 29, 1935. e. USSELMA N2,013,820

PHASE RQTATION DETECTOR AND FREQUENCY REGULATOR I Filed Dec. 10, 1952 eShets-She t 3 PHASE (Of/5721A FREQ 501/1955 INVENTOR- GEORGE L. (155 l,MAN.

ATTORN EY- Oct. 29, 1935. a. L. USSELMAN 2,013,820

- PHASE ROTATION DETECTOR AND FREQUENCY REGULATOR Filed Dec; 10, 1932 6Sheets-Sheet 4 P/l/IJE 1707177011! DETfCTO/a Mam/Ir sou/ms JUZ/RCEINVENTOR- GEORGE .LUSS ELMAN ATTORNEY- Oct. 29, 1935. G. 1.; USSELMAN2,018,320

PHASE ROTATION DETECTOR AND FREQUENCY REGULATOR I Filed Dec. 10, 1932 6Sheets-Sheet 6 706E27/ I I v 71/55 28- Q I INVENTOR- GEORGE L. USSELMANATTORNEY- Patented Oct. 29, I R Q PHASE ROTATION DETECTOR AND FREQUENCYREGULATOR George L. Usselman, Port Jefferson, N. Y., assignor to RadioCorporation of America, a corporation of Delaware Application December10, 1932, Serial No. 646.674

20 Claims. (01'. 250-30) This invention relates to a method of and and anew and improved means for utilizing the means for comparing twoalternating current component energy resulting from said detectionfrequencies. due to reiativeshift between the frequencies This inventionalso relates to a novel method compared to control one ofsaidfrequencies. of and means for comparing two alternating Another, objectof the present invention is to 5;

' currents of high frequency as to frequency and provide an arrangementas briefly described in' of producing energy representative of relativethe preceding paragraph in which tuned circuits shifts in frequency ofsaid alternating currents. are unnecessary and in which thermionic tubesThis invention also relates to a novel method of the triode type areused so that the circuits In of and means for comparing twoalternatingcurare applicable to comparison of and control of rents ofhigh frequency as to frequency and of comparatively high frequencies.producing energy representative of relative shifts Briefly, the aboveobjects are attained in acin frequency of said alternating currents, andof cordancewith the present invention by the use utilizing the energy soproduced to control the of a source of low power constant frequencyenfrequency of one of said currents in a sense ergy of comparativelyhigh frequency connected which tends to maintain said currents instatus. in phase to the input electrodes of a pair of quo over anindefinite period of time. thermionic tubes in a phase rotationdetector.

More in detail, this invention relates'to detec: The tubes have theiranodes connected in outtors in general, and more in particular to phaseof-phase relation to a frequency source to be 2o rotation detectorswhich detect and indicate compared and controlled. The constant fre-.relative phase rotation between two alternating quency source and thesource to be controlled current frequencies, and in so detecting andinshould be substantially equal in frequency but dicating' produceenergies representative of the in operation it is assumed they maydiffer by direction of shift between said two alternating a beat notewhich may vary between, say, 0 and current frequencies, which energiesmay be uti- 10,000 cycles per second. Since the frequency 25 lized tocontrol the frequency of one of said curto be controlled is applied tothe two anodes in rents in a. sense which tends to maintain saidout-of-phase relation (assume about-60" shift) frequency the same as thefrequency of the other two low frequency ,beat notes of equal frequency,oscillation. The frequencies compared may, for which may vary if thefrequency to be controlled o purposes of illustration, be taken as asource of varies, are produced. The beat notes will have constantalternating frequency of relatively a constant phase diiferencedetermined by the small amplitude and a. transmitter frequency. phaseshift between portions of the frequency to that is, a carrier frequencyof a radio transmitter be controlled as applied to the anodes of the ofconsiderable amplitude, the object being to phase detector tubes. Theamount of phase dif- 5 maintain the transmitter frequency constantference between the beat notes never changes without the, use of crystalcircuits connected though the frequency may change. If the fretherewith,etc. r quency relation between'the constant frequency Phase rotationdetectors have been known in source and the source-to be compared andconthe prior art. In general, it has been the practrolled changes fromabove to below or vice versa In tice in the prior art to use tunedcircuits and the phaserelation between the beatnotes will 40 audiofilters to select the operating band of the change, that is reverse. Areversal of 'phase retransmitter. In some cases this latter schemelation between the beat notes takes place each was not entirelysatisfactory since the circuits time the frequency to be controlledpasses had false operating points which permitted the through theconstant frequency. The anode transmitter to operate on the wrongfrequencies. circuits of the phase rotation detectors are cou- 45,Furthermore, the tuned circuits limited to some pied to a trippingcircuit which is actuated in extent the frequency range of the controldevice. "one direction or the other by the phase spaced In other casesscreen gridtubes are used-in the beat note currents of equal but varyingfrephase rotation detectors. For example, see quency in said detectoroutput circuits, the'di- United States Application No. 638,321, filedOctorection of the actuation being determined by the 50 ber 18, 1932. Ihave found that the screen grid direction of the phase or frequencyshift of the type of detector in some cases is not efficient atfrequencies from the transmitter. very high frequencies. The trippingcircuit "or relay is of the type An object of the present invention isto prodescribed in application Serial'No. 380,447, filed vide a new andimproved phase detector circuit July 23, 1929. The phase detector, asbriefly ill circuit.

described above, is coupled by-way of separate audio frequencytransformers to the control elements of two thermionic tubes in thetripping The two tubes have their anode and control electrodes crossconnected by resistances in such a manner that an increase of current inone anode circuit applies negativepotential to the control grid of theother tube and results in a positive decrease .in conductivity of theother tube and decrease in the current in the other anode circuit Thesetubes are normally biased to aj'point at which the desired trippingaction takes place when the potential on the grids changes. The phaserelation between the beat notes determines which tube will be conductivefirst, and, due to the cross-connected resistances, the instant one tubestarts to draw the more current, the other tube is biased more n sbiasesthe control grid of the other tube to a value to cause it to drawcurrent heavily. This applies negative bias to the control grid-of thefirst tube and trips current to the second or other ao aeaoresultinthetrippingclrcuitremaininginone. position of stability foratime suiiici'ent to move the tuning control entirely out of the range ofthe phase rotation detector and/or the tripping circuit.

A further object of the present invention is to provide means wherebythe. normal function of I the relay or tripping circuit, as-described insaid application referred to above; is inhibited under certaincircumstances-as, for example, a failure of the phase rotation detectorcircuits, the refer--- ence frequency source, or of the source ofoscillations to be checked. a

Novel means'is also provided in accordance with the present inventionwhereby, in case of 15 failure of the-currents of varying phaserelation- 4 .9, for any reasonwhatever, the trippi circult is thrown outof normal operation so that atively and draws less current, and the flowof tube. Theaverage current through-these tubes will be greater in onetube than it will be in the other. mined by the relative phase rotationof the transmitter and monitor frequencies, as will be explained laterin detail.

The tripping circuit, desc bed more in detail hereinafter, includes inits 0 tput relay windings connected in opposition so that when theaverage current predominates in'one tube, as briefly descrlbedabove, onewinding is energized exces- The sense of this unbalance is deter-. v V

positions of stabili yahas in a sense three posisively and the otherwinding becomes deenergized to a great extent due to the decrease oftongue or contact closing device may in tin'n control a motor to rotatea tuning element in the transmitter circuit in one sense or the other,

the sense in which this'timing element is being turned depending onwhich tube in the ,tripping circuit is drawing the most average current.The

latter, of course, depends upon the sense of the constant phasedifference between the two equal frequency currents or beat notessupplied fromthe phase rotation detector and resulting from a comparisonof out-of-phase and in-phase currents in said tubes.

' pended hereto.

the output windings again are set in equilibrium or draw equal amounts'of currents, possibly of m different intensity than during normaloperation, so that the relay tongue contact member controlled therebymay, under its spring bias'or polarizing bias, return to the normalcontrol po-- sition so-that the tuning element associated with. 25 thecircuit to be controlled is not moved. In other words, in accordancewith the present invention, the tripping circuit which, as described Iin the application referred to above, had two all. In the latter casethe relay tongue returns,

by spring pressure, toa position midway between the two stationarycontacts.

The novel features of my-invention have been pointed-out withparticularity in the claims ap- 40h L The nature of my invention and themethod of operation thereof will be best understood from thefollowingdetailed description thereof and therefrom when read inconnection with the 4 drawings, throughout the several figures of whichlike reference characters indicate like parts, and

- Figure 1 shows a phase rotation detection circuit arranged inaccordance with the present 50 invention in combination with a source ofconstant frequency, a transmitter, or work circuit,

4 the frequency of which is to be compared and The pping circuit relaytongueand quency control circuits are so coordinated that when theaverage current is greater in one tube it tends to tune the frequency tobecontrolled. toward the frequency of the monitor so that, if the tuningaction is continued due to the tripping action of the tripping circuit,the frequency of. the source to be controlled will be brought to thefrequency of the constant frequency source. If the tripping actioncontinues longer there will be a reversal of phase relation between thebeat I notes and the average current will be greater in the other tube.This the the other direction. a

controlled, 9. tripping circuit connected with the phase rotationdetector, and control means inter- 55 posted between the trippingcircuit and the frequency determining portion of the work circuit;Flgures2 to 9 inclusive show modifications of the arrangement of Figure1';

Figures 10'to 13 inclusive are curves and graphs on which serveto-explain the theory of operation of the phase detector and trippingcircuit; while 'Obviously, where said relay ,circuit is utilizedto'control a tuning element, failure in any portionof the phase rotationdetector, of the refer-5 ence sourcepor of-the transmitter source might1 Figure 14 shows in detail the polarized relay C.

Before describing in .detail the arrangement of Figure l, it will benoted that in all of the modifia5 cations the schematic diagram and thecircuits thereof may be mvided into seven component parts, which partshave been designated by the reference letters A, B, C, D, E, F, and G.

Part A comprises the-elements and circuit of 7 phase rotation detectorcircuit which is a feature of the present invention. The remainin partsof the figure show how the invention isueed-to correct andmaintain theproper trans.

mitter carrlerfrequency.. v 1g shown in Figure 1.

Part B is the tripping circuit. Part C is a polarized relay made tooperate on .relatively small currents..

Part D is a. pair of contactors.

Part E is a reversible motor.

Part F is the transmitter whose carrier. frequency is to be controlled.

Part G is the monitor oscillator of substantially constant frequency andpower. This oscillator may consist of a low frequency oscillator and anysuitable number of frequency multipliers or amplifiers, or both.

A description of the circuit for detecting the phase shift or relativerotation 50f oscillations from the source to be checked or controlledand the reference source will'now be given.

Detection of the-phase shift or direction of phase rotation isaccomplished by means of a pair of thermionic triode tubes II and 12having anodes 9 and I0, control grids 1 and 8, and filaments or cathodesand 6 respectively. The filament heating currents for filaments 5 and 6of tubes II and I2 are supplied from the secondary winding SW offilament transformer T1 through the quarter wave length choke coils Iand 2, as These choking inductances in each of the filament leads are ofthe electrical length specified for a reas on which will appear more indetail hereinafter. These choke coilsmay be in the form of doubleconductors, one for the supply and the other for return of the filamentcurrent. The midtap of the secondary winding SW of transformer T1 isconnected as shown directly to ground. The ends of choking inductancesor coils I and 2 adjacent the transformer T1 are grounded forradio'frequency potentials through'by-pass condensers 4| and 42 asshown. One end of resistor 3 is connected for radio frequency toboth'sides of filament 5 of tube ll through condensers 5I-5l. Thecorresponding end of resistor 4 is connected for radio frequencypotentials to both sides of filament 6 of tube l2 through condensers52-52. The other ends of resistors 3 and 4 are connected together and tothe oscillator G through the blocking condenser 43.

The grid electrode 1 of tube H is connected to ground for radiofrequencies through the condenser 45. Grid electrode 8 of tube 121sconnected to ground for radio frequencies through condenser 44. Grids 1and 8 are both connected together and. to the negative end of powersource 38 by way of lead 56. The anode electrode 9 of triode tube I I isconnected to one end of the resistor l3. The other end of resistor I3 isconnected to ground for radio frequency potentials by way of thecondenser 41. The anode electrode ill of tube [2 is connected to oneend'of resistor 7 'l4. The other end of resistor I4 is connected toground for radio frequency oscillations by way of condenser 46. Theanode electrode 9 of tube ll is'also connected to a point of highfrequency potential in the transmitter F through the resistor 48 and thephase retarding element 48, and the blocking condenser 5!. The anodeelectrode 10 of tube 12 is connected to transmitter F through the phaseadvancing element 58 and the blocking condenser 5|. In other words,phase shifting elements 43 and 50 are both connected through blockingcondenser 5| to transmitter F.

The two output leads 53 and 54 of phase rotation detectors l2 and I Iare connected to the output circuit between resistor 14 and condenser 46and between resistor l3 and condenser 41 respectively.

' lead 51.

' in some respects to this one has been set forth in considerable detailin U. S. application Serial 5 No. 380,447, filed July 23, 1929. A briefdescription of the tripping circuit will be given herein. Leads 54 and53 from the circuit in unit A are connected to the primary windings l5and I6 of transformers T3 and T4 respectively. The other ends ofwindings i5 and "5 are connected to the positive end of power source 38by way of lead 55 to supply positive potential to the anodes oftubes IIand I2 respectively. One end of the secondary windings "and I8 oftransformers T3 15 and T4 is connected to resistors l9 and 23respectively. The other ends of windings I1 and [8 are connected by lead56 to the negative end of power source 38.

The cathode electrodes 21 and 22 of tubes 21 and 2.8 are both connectedto the secondary windings SW of filament transformer T2. The midpoint ofthis secondary winding SW is connected directly to ground. The otherends of resistors I 9 and 20 are connected to the grid electrodes 23 and24 of thermionic tubes 21 and 28 respectively. The grid electrodes 23and 24 are also connected to resistors29 and 30 respectively. The otherends of resistors 29 and 30 are cross connected to the anode electrodes26 and 25 of tubes 28 and 21 respectively, as shown. The anodeelectrodes 25 and 26 are also connected to resistors 3| and 32respectively. The

other ends of resistors 3| and 32 are connected to the coils 33 and 34of polarized relay C, as shown in Figure 1. The other ends of relaycoils 33 and 34 are connected together and to the positive end of powersource 38'by way of The tongue 31 of relay 0 is normally biased toa'neutral position by springs SB and 40 is connected to ground G by wayof the-lead. 58. The showing of the biasing means SB for normallymaintaining the relay tongue 31 in a noncontact closing'position ispurely illustrative-and in no way limiting. In an embodiment constructedand operated a polar relay of the standard Western Electric type wasused. In this relay the tongue 31 is as shown in Figure 14, an extensionof 'a flat spring rigidly fastened to a permanent magnet PM.- The tongue31 extends between north and south poles N and S, of the magnet tocooperate with the contacts 35 and 36. The armature or tongue 31 ismagnetized by the windings 33 and .34 in the output circuits of thetripping circuit. The windings 33 and 34 may be mounted or supported onthe armature 31 which they magnetize. This relay may be and-preferablyis incorporated in each of the control circuits shown inFigures 1 to 9inclusive of the drawings. Contacts .35 and 36 of relay Care connectedto the coils (not shown) of two contactors in unit D. The contacts ofthe two contactors in .D are connected between the power source 36 andmotor E, as shown. The nature of contactors D and reversible motor .E

is not shown since they may be of any suitable transmitter F.

the antenna Iii.

in 'll represents' the work cir cult which may be anantenna connected toOther load circuits may replace Transformers Ti and T2 aresupplied with60 cycle power from some external source. An intermediate point of powersource 38 is grounded. as shown in Figure 1, so as to provide a sourceof both positive and negative. voltage..

Assume that all cathodes are properly heated and that all grids andanodes areprovided with proper potentials. Also assume that power ofconstant frequency and substantially constant amplitude isbeing suppliedfrom (land that transmitter F is operating within the range of "afrequency equal to the frequency of the source G or differing fromthe-frequency-of source-G by less than 10,000 cyclesper second.

Cathodesland 6. of tubes H and I! will receive high frequencyalternating voltage from the reference source G through condenser 43,resistors 3 and 4, and blocking condensers ii-Jl, 52-52. This excitatiouvoltage is prevented f irfqu e ncy comparing and correcting device, Lie,5 U

-. from escaping to ground by the action .of' the choke coils I and 2,which areelectrically substantially one-quarter wave length long with"respect to the'monitor frequency from G. Since grids 1 and 8 arenegative with respect to oath-=- odes 5 and 6 and are grounded foralternating currents and voltages, the excitation energy supplied to thecathodes will be repeated and amplifled by the action of tubes II and I!so that a greater amount of energyof the "monitor fre-- .queney appearson theanodes 9 and ID of tubes H and I 2. Since the excitation" voltageon the cathodes is cophasal, that is, of like phase, the amplifiedenergy of monitor frequency appearing on anodes 8 and ID will also becophasal. Anodes 0 and ID are also supplied with aitemating voltage orexcitation energy from the transmitter F through the phase shiftingelements! and ID.

The frequency of this energy usually will bea little higher or' lowerthan that of the, monitor G. The phaseshifting elements and B0 are setto split the phase of the transmitter excitation on anodes 9 "and i0,"atthe optimum angle for best efficiency of the detector. We willasadvanced 30 degrees by the phase shifting elemore in detail in mUnited States application Serial No. 623.558.'flled July 20, 1932.

same, for the sake of argument, that this phase shift is 60 degrees. Inother words, the excitation from the transmitter F on anode Il'is Thecurrent flowing in anodes 9 and IQ of tubes II and I2 will both bemodulated by both the monitor frequency and the transmitter fre,-quency. Ifthere is a normal amount of frequency difference between thetransmitter and the. monitor, equal audio or low frequency beat .noteswill appear in the anode currentswf both tubes I I and i2. However. theaudio components in these two tubes will have a 60 degree phasedifference due to the-assumed 60 degree phase. difference in eexcitation by. the oscillations from transmi Fon' of equal amount andlike phase from the substanamegsao In proceeding furtherwith;.the"theoryofthe invention, reference ,willbe/made to Figure 10.The phase rotation detec tbr cathodes are each supplied with radiofrequency current and voltage tially constant frequencyoscillator ormonitor.

I This energy maybe represented -by-tlr'ijvector M in Figure 10. Theanodes of the phase rotation detector each receive equal amounts ofradio frequency current and voltage from the transmitter whose frequencyis to be controlled and compared with the monitor frequency. However,the two portions of the energy supplied to the anodes from thetransmitter passes through two phase shifting devices so that the phaseof the energy supplied to one anode is advanced a certain amount and thephase of the energy supplied to the other anode is retarded or lags acertain amount. The portions of energy supplied to the first anode maybe represented by vector I 0 in Figure 10, and the-portion of energysupplied to the second anode may be represented by the 1 vector 9 inFigure 10. Now we may assume that the frequency of rotation of monitorvector M is F1, and that the frequency of rotation of both vectors 9 andIll (transmitter frequency) is F2. But since there is a constant phasedisplacement between the two portions of energy supplied by thetransmitter to the two anodes of the phase rotation detector tubes, wecan represent the lagging portion, or vector'S, as having a frequencyand phase relation of F2 -0/2. and the leading portion, orlvectori0,'@as having a frequency and phase relation of F2+0/2. The total phasevdifierence between portions 9 and I0 is 0.

This is constant and is fixed by the phase shift ing elements It, 49 and80. Y I

The side bands of these two frequencies may. be represented by F1+Fa,and F1Fa or Fz-F1. We are interested only in the lower frequencies FiF2and :F1. If frequency F1 is higher than F: then a low frequency beatnote will be Fi-Fz. If frequency F2 is higher than F1 then the lowfrequency beat note will be F's-F1. This can be visualized byconsidering vectors -9 and I0 as standing still and for frequencieswhere F1 is higher than Fz vector F1 will rotate counterclockwise at anaudio or beat frequency rateof Fi-F2. Likewise,'for frequencies where F:is I higher than Fr the vector F1 will rotate clockwise o at a beatfrequency rate of Fa-Fr.

Now consider frequency F1 higher than F:

.(counter clockwise rotation of vector M relative. vectors 8 and II),the beat. frequency of vectors I M and 8 will be F1-(F:0/2 and the beatfre quency of vectors M and I0 will be F1'-(Fa+0/2) This gives two equalbeat frequencies having a phase difference of angle 0. In this casethebeat frequency of vectors M and. 9 is leading that'of vectors]! and II'bythe angle 0.

However, when frequency F2 is higher than F1,

' vector M clockwise, relative to vectors 9 and". at beat frequency rateand by the sameprocess of reasoning it can be seen that we will againhave two equal beat frequencies having a 05 phase difference ofangled-but in this case the beat frequencyof vectors M and I0 is leadingthat of vectors M and i by the angle 0. 7 It should be noted that as thetransmitter frequency, changes relative to the monitor frequency 70.

the frequency of both beat notes (phase rotation detector outputs)change but are always 4 equal and have a constant phase difference. Thephase relation of' the two beat notes'reverses as the beat zero. This isevident lmanner. This would give two sine waves a and b having a phased'iiference of as illustrated in Figure 11.

The alternating component of one portion of the energy delivered by thedetector passes through transformer Ts in Figure 1 to the trippingcircuit, and the alternating current component of the other portion ofthe energy delivered by the detector passes through transformer T4 inFigure 1 to the tripping circuit. It should be remembered thattransformers of iron core type also act as filters, that is, they arevery ineflicient or will not pass extremely high or very low frequencyenergy.

, If the amount of phase split is increased or decreased, the amount ofphase difference in the low frequency component of current in anodes 9and ill will be correspondingly increased or decreased. These two out ofphase low frequency compo- 'nents are transmitted to the trippingcircuit B and act as a high impedance for low frequencies so that thelatter are passed on to the next stage, while the high frequencies areabsorbed by resistors l3 and i4 and condensers 41 and 46.

The audio output of detector tube ll passes through the primary windingl5 of transformer T3 and the audio output of detector tube l2 passesthrough the primary winding 16 of transformer T4. This audio voltage ishere transformed and again appears in the-secondary windings I1 and I8of transformers T3 and T4- I Now the action of trippin circuit B is thatwhen there are no disturbing variations inthe circuit voltages, only oneof tubes 21 or 28 will draw current. When the plate and grid voltagesare first applied, both tubes will start todraw current, but due to theconstants and peculiarities of this circuit, the first tube drawing themore current will cause the second tube to be biased to cut ofi. Thesecond tube, which is being cut oif, will cause the grid of the firsttube to become more positive. The result is that the current willpositively trip to one tube. If the grid of the second tube, which isnot drawing current,'be given a positive kick suilicient to overcomethefirst tube which has been drawing current, the circuit current willtrip to the second tube and stay locked in the last position until apositive kick on the grid of the first tube again restores it to theoriginal condition. If we put two equal alternating voltages ontransformers Ta and T4, sufficient to operate the tripping circuit, andhaving 180 degrees phase difference, the average current in each side ofthe tripping circuit-will be equal. Now if we change this phasedifference to 60 degrees, aswe have assumed in this case, the currentson the two s des of the tripping circuit will be unbalanced. The tubewith leading phase will carry current the smaller part of the cycle andthe tube with lagging phase will carry current the larger part of thecycle. This unbalance is caused by the fact that each tube carriescurrent over the phase angle until the next tube trips the circuit. Thusin the assumed phase adjustment the leading tube and lagging tube wouldhave an average current ratio of about 60/300 if other constants in thecircuit do not-tend to decrease this ratio.

Now the phase rotation" detector supplies two alternating voltages tothe tripping circuit. These two alternating current voltages can be 5adjusted to have a-phase difference of less than 180 degrees as I haveexplained before and we have assumed a setting of 60 degrees. Also, as Ihave explained before, as the transmitter frequency passes through themonitor frequency, 10

the position. of leading and lagging phase is reversed. This causes thetripping circuit current to become unbalancedin the opposite direction.This operation will be better understood if we assume an instant in theoperation of the tripping l5 circuit when tube 28 is drawing current andtube 21 is blocked off, and thatfrequency F1 is higher than F2. When thevector sum of vectors M and 9 become great enough, the potential of grid23 of tube 21 will be "kicked" far enough positively to overcome thelocking bias imposed on it by tube 28. Instantly the circuit trips sothat tube 21 is now drawing heavy current and tube 28 is blocked ofl.This locked condition continues until vector M (still rotating counterclock- 25 wise) approaches vector l0. When the vector sum of vectors Mand I0 becomes great enough the potential of grid 24 of tube 28 will bekicked" far enough positively to overcome the locking bias imposed on itby tube '21. Again the circuit instantly trips so that tube 28 now drawsheavy current and tube 27 isblocked off. The circuit now stays trippedor locked in this position until vector M rotates around the major partof the revolution and again approaches vector 9 when the cycle will berepeated. In other words, tube 2! draws current over the angle 0 andtube 28 draws current over the angle 360-0. Figure 12 illustrates theblocks of current drawn by the tubes in the tripping circuit whenfrequency F1 40 is higher than Fa.

If frequency F1 is lower than F: the vector M will rotate, as explainedbefore, clockwise relative to vectors 9 and I0. Using the same line ofreasoning as above,.tube 28 now draws current over the angle 0 and tube21 draws current over the angle 360-0. Figure 13 illustrates the blocksof current drawn by the tubes in the tripping circuit when frequency F1is lower than F1.

- Since the anode currents of the tripping circuit pass through thecoils of the relay 0, as shown in Figure 1, the relay tongue 31 will bethrown on one side or the other. This operates the contactors D througheither contact 35 or 36 of relay C, depending on the position of therelay tongue 31. Contactors B may be connected to the reversible motor Eso that it will operate always to correct the frequency of transmitter Fthrough the tuning means 39.

If we employ a constant frequency oscillator he phase rotation detectorcircuit A operating through tripping circuit 13, relays C and D andmotor E, will operate to maintain substantially constant frequency inthe transmitter F.

Referring again to Figure. 1, the reason for using three element tubesinstead of screen grid bes in the phase rotation detector circuitA isthat the three element tube is a much better detector, especially whenexcitation must also be appliedto the anode of the tube. The threeelewent tube gives much greater detector response. The purpose of theradio frequency grounded grids of these tubes is to introduceelectrostatic shielding between the anodes and the cathodes.

- This uncouples or rather prevents capacitive the anodea'. There issome coupling between the cathode and the anode due to thetubecurrentbut this does not cause any trouble, and it is relatively small comparedwith the capacitive coupling which would exist athigh frequencies.

if the grids were not grounded. 1

I have. not stated previously the purpose of resistors 3 and 4.; Theseresistors absorb some of the monitor energy and are detrimental to asmall extent but they are quite necessary to reduce the coupling betweencathodes I and 8. If the cathodes are closely coupled together, theanodes 9 and ID will also be sumciently coupled together through thetube currents to interfere.

with the action of the phase splitting circuits.

The use of resistors 3 and 4 reduces this coupling action of the phasesplitting circuits containing elements 48, 48 and so. In practice it ispreferable that non-inductive resistances be used in circuit B andimperativethat non-inductive resistances be used in circuit {A forproper operation of the invention at high frequency. i In other words,all of the resistances connected with tubes (I I, I2, 21 and should benon-inductive, while all of the resistances connected with tubes I I andI! must bench-inductive to obtainbest results.

The specific embodiment of the present invention, as illustrated'inFigure 1, may. be modified by using either an inductance and acapacitydor phase shifting elements 49 and 80, or I may use, linesofdifierent electrical length for this purpose, as illustrated in-myUnited States application Serial No. 607,932, filed April 28, 1932.Other circuit. modifications may be made without departing from thescope of the invention.

When the phase detecting means; as illustrated in Figure 1, is used tocheck the frequency of a telegraph transmitter having a singleoscillator frequency range of the frequency regulator oirstage, noexcitation voltages are supplied to the phase detector by thetransmitter when the transmitter is not keyed. During long intervalsbetweensignals this might permit the tripping circuit B to run thefrequency determining condenser 39 past the point at which it tunes itscircuit to the correct frequency. e condenser asmight tune the circuitto .a frequency out of the cult AB. Under these circumstancesthetripping circuit current will continue to flow in that tube 28 or 2'Iin which it was last caused to how by the action of the phase rotationdetector circuit ll, l2,'l3, [4 etc.

The same thing occurs: if the excitation voltage from monitor G for anyreason fails. Also when the transmitter F is keyed or, rather, when thekey in Fis opened and the signal'from the trans- 'mitter' is stopped,transformers Ta-and T4 often give ar'everse kick or pulse of currentwhich reverses the action of theftrlpping circuit 1B,.and during thistime when the signal is oh, condenser 39 is.turned the wrong direetionfor, correcting the frequency of the transmitter F. This actioncontinues until the signal is again put on, at

which time the frequency of the transmitter F maybe completely outsideof the operative fre-.

"'quency-range of the regulator circuit. In order to stop this incorrectoperation of the'frequency regulator it is necessary to stop the actionof the tripping circuit .8 when the phase rotation deaoiaeao tector Aisnot producing proper output potentlals. Means are provided in accordancewith the presentinvention to stop the action of the .trlpping circuit Bwhen there is no output from the 5 frequency outside of the range of theregulator.

This is accomplished by connecting a resistor il in the filament returnof the final stage of the transmitter. A tap from this resistor isconnected to the midpoint of the secondary winding of transformer 63which furnishes heating .current for the filament of a modulatortube-64. The grid to of this modulator tube is connected 20 to ground. eplate "of the modulator tube is connected the direct current source 88which supplies potential to the plate of the tubes in the trippingcircuit by way of a resistor R. This resistor R is also connectedbetween the power sup- 2& ply 38 and the plates 25, 26 of the tubes inthe tripping circuit B. Now, when the transmitter is keyed and sends outoscillations, current will flow in the filament return including theresistor ii. The potential of the filament of so the modulator tube 64will swing positiverelative to the potential of the grid electrode 85since the grid electrode is at ground potential. This results indecreasing the conductivity of tube 84 and the plate current of thismodulator as tube will be decreased. Under-these conditions the tube 54places no additional load on the source". allows the tripping circuit tofunction normally. Conversely, when there is no signal sent out by thetransmitter the filament of the modulator 'tube 84 will be less positivebe- "cause there is less potential drop in 6|, the consprings BS bringthe tongue to a central noncontact closing position. This is the actiondesired.

p In cas'ethe monitor oscillator or circuits be-oo tween said oscillatorand the phase detector A fail, the'tripping circuit may cause thecondensex- 38 to tune the transmitter to a frequency outside of theregulator range. To prevent this from taking place the arrangement ofFigure 3 may so be used.- In Figure 3 ,a .thyratron rectifier, comprisestwo tubes V; and V2 with their plate electrodes grounded through thecenter tap of the secondary winding 10 of the transformer T0, theprimary winding of which may be connected to any low frequency source ofenergizing. current. The cathodes or filaments I2 and 13 of V1 and V2are connected by lead f3 to the relay coils 33 and 34 in the trippingcircuit and supply rectified alternating current to the tubes Hand 28 ofthe tripping circuit. The grids 14 and 15 of the thyratron tubes VrandV: are normally biased to cut-oft bythe negative voltage source 16connect- 'ed thereto by way of resistance 11, and they also receiveexcitation potentials fromthe phase rotation detector A. Thesepotentials may be recelved directly from A or, if desirable, through a200 cycle high pass filter", as shown, and through a blocking condenser18, or an audio lo This rectified current potential is applied from thecathodes 12 and 13 to the tripping circuit by lead 13', thereby allowingthe .tripping circuit to operate in a normal manner. If either themonitor G, or the transmitter F stops, this thyratron rectifier willalso stop since no excitation is supplied to the grids thereof from A.This prevents the tripping circuit from operating unless G, F and A areoperating normally. In some cases this circuit may not be satisfactorybecause of the ripple produced by the rectifier. Of course, smoothingcircuits could be applied but then the rectifier might not follow thetransmitter keying suiiiciently close to obtain the best results.

In Figure 4 I have disclosed an arrangement which includes all of thedesirable features of the arrangement of Figure 3 and none of thedefects thereof. In Figure 4 the plate power supply lead 51 of thetripp'ng circuit passes through the normally closed contacts 88 of adirect cur-' rent relay. The actuating winding 8| of this relay is inthe anode circuit of tube 82 and in this winding fiows the current tothe anode 83. of

\ relay tube 82. The filament 84 of tube 82 is connected to ground asshown and to a filament power supply source not shown. A by-passcondenser 85 allows. the audio component of the anode to filamentcurrent to fiow directly from anode 83 to cathode 84. The tube 82 isbiased to cut-01f by maintaining a proper negative voltage on grid 86from bias source 18 through resistor.

11. The grid 86 of tube 82 receives excitation voltage from the phaserotation detector through the high pass filter 19 and direct currentblock:- ing condenser 18. Here, as in Figure 3, a coupling transformermay be used to couple the high pass filter to the grid electrode 88 oftube 82. The high pass filter may have a lower limit of approxmately 200cycles per second.

In operation, since tube 82 is normally biased to cut-off when noexcitation voltage is applied from A, tube 82 will not rectify or passanode to cathode current and contact 88 will be open as shown. When thegrid electrode 86 receives excitation voltage from A by way of the highpass filter the normal blocking bias will be overcome and tube 82 willpass current. This current energizes coil 8| and causes it to actuateits armature 88 to close the path between the anode of the trippingcircuit and the anode source 38. T1118 allows thetripping circuit tofunction. When the excitation voltage from A stops tube 82 is biased tocut-ofi by 18 and 11 and the tripping circuit also ceases to functionsince the current in lead 51 is interrupted. The high pass filterblocks, off all low frequency so that the frequency regulator stopsregulating through a band 408 cycles wide about the correct frequency,as detel-mined by the frequency of .the source G.

In practice it has been found that the relay 8|, 88 of this circuit maynot in all cases be sens'tive enough to follow with the high speedkeying operations. A regulator circuit of the type describedhereinbefore, and which includes all of the advantages of thearrangements described before and. in addition, a control means sensi--tive enough to respond to high speed keying, has been illustrated inFigure 5. In this modification of the frequency regulator circuit, the

biasing voltage for the control electrodes 23 and 24 of tubes 21 and 28in thetripping circuit is supplied from the common source 38 through theanode to cathode impedance of tube 88 and the primary winding P oftransformer T. The cathode electrode 89 of tube 88 is connected to thenegative terminal of the common biasing source 38, while the anode 98 oftube 88 is connected as shown to the winding P of transformer T. One

end of the secondary winding S of transformer T is connected as shown tothe cathode 89 of tube 88. The other end of secondary winding S isconnected through the filter condenser 9| and negative bias source 92 tothe grid 93 of tube 88. Load resistor R1 is connected as a load acrossthe secondary winding S of transformer T. The resistance R2, which maybe replaced by a reactor, completes the direct current circuit betweenthe positive end of bias source 92 and cathode 89 of tube 88. By-passcondenser 94 furnishes an alternating current path for the grid tocathode circuits of tubes 21 and 28 around the mpedance of tube 88.

When there is no energy in the output from the phase rotation detector,tube 88 is blocked to 25 cut-Qofi by source 92 so that the directcurrent biasing circuit of tubes 21 and 28 includes the highimpedance ofthe tube 88 and the negative bias voltage is cut-01f from the tubes 21and 28 in the tripping circuit. Consequently, tubes 21 30 thealternating current from the phase detectors is applied to thetransformer T and from there to the grid 93 of tube 88 to overcome thenormal negative has applied thereto. conductive and the grid tocathode'circuit of the tripping circuit is supplied with normal negativebias instead of positive bias. Under these circumstances a change inphase relationship of the audio currents in T3, T4 starts a trippingaction in 23 and 24. Consequently, the tripping circuit functions tooperate the relay and frequency correction occurs when necessary. Thiscircuit has proven successful inoperation.

The regulator circuit of Figure 6 is similar to the one describedimmediately above,and illus-v same as the circuit illustrated in Figure5 and described above. I

Another modification of the frequency regulator circuit is shown inFigure 7. This circuit, and the operation thereof, is substantiallysimilar to the circuits described above and in particular to-thecircuits of Figures 5' 'and- 6. The present circuit, however, isdifferent in. that .the

Tube 88 becomes 45 grid sass-a. a: "6: adj realm its I excltationvoltages from 'the resistor R1, in the lead 155 between the phase.rotation detector plates and the plate supply 88, through the directcurrent blocking condenser 18. Negative potential sufficient to biastube 88 to cut-off! is supplied from the source 82 through reactor X tothe control grid 88 of tube 88. Here,v as in Figures and 8,

when no excitation voltage appears in the output circuit of the phaserotation detector A. the control-grid of tube 88 is maintai at anegative value sufilcient to bias 88 to on -ofl so that the highnegativepotential from source88is preplied" to the control grids of tubes 2l and28.

vented'from reaching-the control grids 28, 28 of tubes 21, 28respectively. These grid electrodes are at equal positive potential andequal currents flow in the windings 88 and 84 so that the armature 81stays-in its centralposition at The tripping circuit functions inaccordance with the relative phase shift between the oscillations from Gand-F and the transmitter frequency is corrected. When; for some'reason,it ismore-preferable to determine the operativeness of the trippingcircuit by controlling the impedance of the anode circuit thereof ratherthan the grid circuit thereof, the arrangement oiv Figure 8 may be used.

The operation of this circuit is fun general way.

similar to the operation of the circuits described above, and inparticular of the circuits illustrated in Figures 2, 3, and 4.- In thiscircuit, however.

. the primary windingP'of. transformer T is con- .leadn55' of the phaserotation detector.

,w inding P is connected also load resistonRr and a low pass filterwhich shunts most of the 200.

flected in series with the plate or anode supply cycle alternatingcurrent component around winding P. I One end of the secondary winding 8of transformer T is connected to ground and to the cathode; of tube 88.The other end of winding S is connected to the. grid 88 of tube 88through the biasing grid leak resistor Re and condenser C3. The lattertwo elements are connected in parallel..;. The anode 88- of tube 88 isconnected to the positive supp y lead 81 of the tripping circuit. Theresistor R is connected between the positive terminal-of'the powersupply source 88 and the anodes .of' tube 88 and tubes 21 and 28 of thetripping circuit. when there is no excl- .tation voltage in the outputcircuit of the phase- .-rotation detector, or when its output frequencyis too high to passthrough the transformers T, T:

and T4, or when the output frequency is too low and is shunted out oftransformer T by the low pass filter LPF, then there is no'excitationenergy on the control grid 880i tube 88 d its plate or I anode currentis maximum; This space current whichfiowslin tube .88.,causes sumcientvoltage drop in resistorR to lower the potential-on anodes 25 and 28 oftubes 21 and 28 and cause the anode current in the tripping circuittubes to be low .orcut off. -.Then. since there is no current in thecoils 88 and 84 of the polar relay. the relay tongue 81 remains in themidr-posltion touching neither output from the ph Acrosscontact 88 nor88- due: tothespring bias so that the frequency correction remains f- Istationary. when there is alternating current;

agrotation detector, trans formed by transformer T, excitation voltageis 5 applied to grid 88 of tube 88. This causes the tube 88' to bebiased by the rectified grid current passing through the grid resistorB: so that the anode current of tube 88 is thereby reduced. 0 Thisreduction in tube 88 anode current decreases 10 the drop in R andconsequently increases the volt- 1 age applied to anodes 28 and 28 oftubes 21 and 28 in the tripping .circuit. The rise in anode voltagecauses normal-anode current to fiowin the tripping circuit and it then"functions nor- 1!; mally to correct the transmitter frequency.

The arrangement illustrated iii-Figure 8 may "be modified as indicatedin Figure 9. The circuit in Figure 9 is different in that the grid 88 oftube 88 is supplied with excitation voltage from the 20.

resistor R3, which is connected in series with .the anode supply lead 55of the phase rotation detector.

rent blocking condenser 18 and the parallel com- 85 bination Of'Ca' andR: to the grid electrode 88 of tube 88. The reactor X is connectedbetween the requirement that the tongue 81 of the polar relay returns tothe central position touching 5 neither contact when .equalcurrents flowin its coils 88 and 88 or when no current flows in the coils 88 and 88.When the relay is properly ad justed a spring SB holds the relay tonguein midposition when the tripping circuit-is not func- 40 tioning. I Themodified frequency regulator will function to correct the transmitterfrequency when both the monitor andthe transmitter are operating, if thebeat frequency between-the two is not too high or too low to passthrough the transformers and filters to the tripping circuit. During theinterval between signals, or if the monitor stops functioning, thefrequency regulating or correcting circuits will remain inoperative. Ifthe beat frequency regulator quite fool proof and reliable.

It should be remembered that the function of this invention is to keepthe transmitter frequency tuned or regulated closely to that of thecrystal monitor output. The monitor can be made small in dimensions and'of greatfrequency constancy at moderate cost and the. phase rotationdetector and tripping circuits are also inexpensive, where as acrystalj'controlled transmitter is usually? very expensive incomparison.

.. :Having thus described my invention and the 55 operation thereof,what I claim is:

1. The combination with a thermionic relay having a high frequencyoscillation circuit including tuning means, of means for controllingsaid tuning means to maintain the oscillations of" said circuit ofconstant frequency irrespective of any tendency of said oscillations toshift in phase or frequency which consists of a source of oscillationsof constant frequency. thermionic devices,

for .demodulating superimposed oscillations the The excitation energyfrom the phase I rotation detector passes through the direct our--relative phase of which may shift, coupled in parallel to said source ofconstant frequency, circuits coupling said devices with said oscillationcircuit, an additional circuit coupled with said thermionic devices andenergized by energy produced by the demodulation action thereof, anddriving means operatively interposed between said additional circuit andsaid tuning means, said driving means being actuated by energy in 10said additional circuit.

2. A phase rotation detector comprising, a pair of thermionic tubes eachhaving ,a cathode, an anode and a control electrode, means for grounding said control electrodes for high frequencies, means for applyingconstant high frequency oscillations in phase to the cathodes ofsaidtubes,

and means for applying the oscillations to be detected in unlike phaseto the anodes of said tubes. 3. A phase rotation detector comprising, a

pair of thermionic tubes having their control electrodes groundedthrough condensers, in-

ductances connected between the cathodes of each of said tubes andground, means for applying constant frequency oscillations to saidcathodescathodes of each of said tubes and ground, cathode heatingcurrent being supplied through said inductances, a phase shiftingcircuit for applying the oscillations to be detected to the anodes ofeach of said tubes in unlike phase, a separate anode circuit for each ofsaid tubes, said anode circuits including diiferential windings, and autilization circuit coupled with said windings.

5. The combination of a phase rotation detector connected on the onehand to a source of constant frequency oscillations and on the other ahand to a transmitter having a frequency determining circuit including amovable element, driving means connected with said element, and a Ithermionic tripping means interposed between said phase rotationdetector means and said driving means comprising, a pair of thermionictubes having their input electrodes connected in separate inputcircuits, resistive means connecting the input circuit of each of saidtubes to the output circuits of the other of said tubes, and a relayhaving a winding in each of said output circuits, and an armatureresponsive to currents in said windings cooperating with contacts in theenergizing circuit for said driving means.

6. A circuit adapted to convert currents of va y g phase relation intocharacteristic currents comprising, a pair of thermionic tubes, an inputcircuit connected with each of said tubes, said input circuits eachbeing energized by one of said currents to be converted, resistive meansconnecting the input electrode of each of said tubes to the outputelectrode of the other ofsaid tubes, output circuits connected to theoutput electrodes of said tubes, a pair of windings, said windings beingconnected in opposition in the output circuits of said pair of tubes, acircuit for normally biasing the control grids of said tubes to a pointat which equal currents flow'in said output circuits when no currentsare applied to saidinput circuits whereby equal and opposite currentflows in said windings, said output circuit including an impedance in acommon portion, and means connected in parallel with said impedance andactuated by the presence of currents to be converted in said inputcircuits for decreasing the current through said impedance to increasethe positive potential on the output electrodes of said tubes.

"7. Means for converting variations in currents 10 of one of saiddevices being connected to the anode of another of said devices and theanode of said last named device being coupled to the control electrodeof ,said first named device whereby an increase in the current in theanode circuit of one of said devices causes a decrease of current in theother of said devices, and a circuit coupled to said tubes and actuatedby said currents to be compared to render said electric circuit anddischarge devices operative only when said currents are impressed onsaid input circuits. 8. Means for converting variations in phaserelationship between two currents into impulses of characteristic sensecomprising, a pair of thermionic tubes, a resistance for connecting theanode of one of said tubes to the control electrode of the other of saidtubes and the anode of said last named tube to the control electrode ofsaid first named tube, means for applying one of said currents'to thecontrol electrode of one of said tubes, means for applying the other ofsaid cur- 40 rents to the control electrode of the other of said tubes,means for normally operating said tubes so that when no currents areapplied to the input electrodes, substantially no currentsfiow in theanode. electrodes of said pair of tubes comprising, a source ofpotential having its positive terminal connected through resistance tothe anodes of said tubes and its negative terminal connected to thecathode electrodes of said tubes, an addi-- tional tube having itsimpedance connected in parallel with said source and resistance, andmeans for increasing the impedance of said additional tube when currentsare applied to said input circuits comprising a transformer having itssecondary winding connected to the control electrode of'said additionaltube and its primary winding energized by said currents to be converted.

9. Means for converting variations in phase relationship between twoalternating currents into impulses of characteristic sense comprising, apair of thermionic tubes, a resistance for con-. meeting the anode ofone of said tubes to the control electrode of the other of said tubesand the anode of said last named tube to the control electrode of saidfirstnamed tube, a transformer for applying one of said alternatingcurrents to the control electrode of one of said tubes, a transformerfor applying the other of said alternating currents to the controlelectrode of the other ofsaid tubes, means for normally energizing theelectrodes of said tubes to a point at which, when no currents areapplied to the input electrodes, substantially no currents flow in theanode electrodes comprising, a source of potential having its positiveterminal connected to the anodes of said tubes through a resistance andits negative terminal connected to the cathodes of said tubes, anadditional thermionic tube having its impedance connected in parallelwith said source and resistance, and means for increasing the impedanceof said additional tube when currents are applied to said input circuitscomprising a circuit including a resistance and capacity in seriesconnected between the control electrode of said additional tube and theprimary windings of said transformers.

1-0. In an electrical apparatus, a pair of thermionic discharge devices,each having an anode, a cathode and a control grid electrode,resistances cross-connecting the anodes and control grid electrodes ofsaid tubes, whereby an increase in anode current of one of said tubescauses a decrease in anode current of the other of said tubes, a dividedrelay coil connected through resistances between the anode of saidtubes, circuits for apship to cause small currents to flow through saidtubes and said coils.

11. In an electrical apparatus, a pair of thermionic discharge devices,each having an anode, cathode and a control grid electrode, resistancescross-connecting the anodes and control grid electrodes of said tubes,whereby an increase in anode current in one of said tubes will cause adecrease in anode current in the other of said tubes, a divided relaycoil connected through resistances between the anodes of said tubes,circuits for applying energy of varying phase relationship throughresistances to the cathodes and control electrodes of said tubes, adirect current source and a resistance for applying a potential to theanodes of said tubes such that said tubes are conductive and unequalcurrents flow in the'two portions of said anode divided winding when thecurrents applied to the input circuits are of varying phase relation,and a circuit responsive to failure of said applied currents of varyingphase relationship for puttingan additional'load'on said direct currentsource, and said resistancewhich will reduce the currents in the relaywindings and anodes of said first tubes, substantially to .zero value.

12. In an electrical apparatus, a pair of thermionic discharge devices,each having an anode, cathode and a control grid electrode, resistancescross-connecting the anodes and control grid electrodes of said tubes,whereby an increase in anode current in one of said tubes results in adecrease in anode current in the other of said tubes, a divided relaycoil connected through resistances between the anodes of said tubes,circuits for applying currents of varying phase relationship throughresistances to the cathodes and control electrodes of said tubes, asource of direct current connected through an additional resistancebetween the anodes and cathodes of said tubes, a second source of directcurrent for applying a biasing potential to the control electrodes ofsaid tubes such that unequal currents flow in the two portions or saiddivided anode winding when the phase relationship of the energy appliedto the input circuits varies, and a circuit responsive to failure'inpart of said applied currents of varying phase relationship for alteringthe intensity of current flow through said tubes and said coilscomprising an additional thermionic tube having its anode connected tosaid additional resistance, a connection between the control grid ofsaid additional thermionic tube and the negative terminal of said firstnamed direct current source and a circuit for biasing the cathode ofsaid additional thermionic tube to a potential representativeof.thecharacter of said currents of varying phase relationship.

13. The combination with a source of high frequency oscillations ofmeans for regulating the constancy of said oscillations comprising, asource of constant frequency oscillations, a pair of thermionicrectifiers having their input electrodes connected in like phase tosaid-source of constant frequency oscillations and their outputelectrodes connected in unlike phase to said source of oscillations, theconstancy of which is to be indicated, a tripping circuit comprising apair of thermionic tubes, each having an input circuit connected to theoutput circuit of one of said rectifiers, resistive means for connectingthe output circuits of said tubes in push-pull relation to relay coils,a resistance connecting the anode of one of said tubes to the controlelectrode of the other of said tubes, a resistance connecting the anodeof said last named tube to the control electrode of said first namedtube whereby an increase in current in the anode of one of said tubescauses a decrease in the anode current of the other of said tubes andvice versa, and means for rendering said tripping circuit inoperativewhen oscillations, the constancy of which is to be determined, areinterrupted comprising a thermionic tube having its internal impedanceconnected in parallel with the impedances of the tubes in said trippingcircuit and means for increasing the conductivity of said tube whenoscillations from said source cease.

14. A tripping circuit adapted to convert audiofrequency currents ofvarying phase relationship into characteristic impulses comprising, apair of thermionic tubes, an input circuit connected throughresistances'with each of said tubes, said input circuits beingseparately energized by said currents to be converted, resistive meansconnecting the input electrode of each of said tubes to .the outputelectrode of the other of said tubes, a

substantially no currents fiow in said-output cirnormally applying aposltive'bias to the control grid of said additional tube, and a circuitfor overcoming said positive bias to apply a negative bias to thecontrol grid of said additional .tube when output electrode of the otherof said tubes, a relay including a pair of windings, said windings beingconnected to the output electrodes of said pair of tubes, means fornormally biasing said tubes to a point at which current flows in saidoutput circuits when currents are applied to said input circuits wherebycurrents flow in said relay windings, a direct current source, avariable impedance, and a resistance for connecting said direct currentsource in series with the output electrodes of said tubes and with saidvariable impedance.

16. The combination of'a radio frequency transmitter including a sourceof oscillations the phase and frequency of which may vary, a frequencycontrolling device connected with said source of oscillations, ademodulating circuit including a thermionic system having its electrodesenergized by cscillations from said source, the frequency of which isdetermined by said frequency controlling device in said transmitter andalso energized by oscillations of constant frequency, a

thermionic relay device coupled to said demodulator circuit andenergized thereby for producing current impulses characteristic of thephase relation of said oscillations, the frequency of which iscontrolled by said frequency controlling device in said transmitter andsaid constant frequency oscillations, a device interposed between theoutput of said thermionic relay and the frequency controlling device insaid transmitter to supply controlling energy from said relay to saidcontrolling device, and a circuit connected with said thermionic relayfor rendering the same inoperative when the oscillations of constantfrequency or of controlled frequency are not. applied to saiddemodulator circuit.

1'7. A phase rotation detector comprising, a pair of thermionic tubeseach having anode, cathode and control grid, circuits of low radiofrequency impedance connecting each of said control grids to ground,means applying constant highfre-- of thermionic tubes having theircontrol electrodes connected together, means for maintaining saidcontrol electrodes at substantially ground potential for saidoscillating currents, a circuit for applying one of said oscillatingcurrents in phase to the cathodes of said tubes, impedances connectedbetween the cathodes of said tubes and ground, and a circuit forapplying-the other of said oscillating currents to be compared in phasedisplaced relation to the anodes of said tubes.

19. In an electrical apparatus, a pair of thermionic discharge deviceseach having an anode, a cathode and a control grid electrode, directcurrent conductive impedances interconnecting the anodes and controlgrid electrodes of said tubes,

whereby an increase in anode current in one of said tubes causes adecrease in anode current in the other of said tubes, substantiallyequal direct current conductive impedances connected between the anodesof said tubes, circuits for applying energy of varying phaserelationship between the cathodes and control electrodes of said tubes,means for applying potentials to the electrodes in said tubes such thatunequal currents flow in said substantially equal impedances connectedbetween the anodes of said tubes when currents of varying phaserelationship are applied to the input circuits of said tubes, and 'acircuit actuated in response to the failure of said applied currents ofvarying phase relationship to cause small currents to flow through saidtubes and said substantially equal impedances.

20. In an electricalapparatusa pair of thermionic discharge devices,each having an anode, a cathode and a control grid electrode, directcurrent conductive impedances cross-connecting the anodes and controlgrid electrodes of said tubes,

whereby an increase in anode current in one of said tubes causes adecrease in anode current in the other of said tubes, direct currentconductive reactors connected'between the anodes of said tubes, saidreactors being connected to the cathodes of said tubes, circuits forapplying energy of varying phase relation to the control electrodes ofsaid tubes, a direct current source connected the currents applied tothe input circuits are of varying phase relation, and a circuitconnected with said source and responsive to failure of said appliedcurrents of varying phase relationship for putting an additional load onsaid direct current source which will reduce the currents in saidconductive reactors between the anodes of said tubes substantially tozero value.

GEORGE L. USYSELMAN.

